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Veterinary Forum June 2009 (Vol 26, No 6)

Dental Dilemma — Can Shadow's Jaw Be Saved?

by Jan Bellows

Shadow, a 3-year-old, 4-kg, neutered miniature poodle,presented for evaluation of apparent puncture wounds below the mandibles (Figure 1). The dog did not live in an area where snake or spider bites were common, and no other companion animals lived in the household. There was no pertinent history of trauma that would account for the lesions.

Physical examination revealed a normal-appearing dog, with a body condition score of 3 based on a 5-point system.

Oral abnormalities noted during the dental assessment included moderate gingivitis and calculus accumulation, especially around the facial surfaces of the maxillary premolars, mandibular incisors, and mandibular molars. In addition, the mandibular incisors were malpositioned and crowded (Figure 2) and two moderately firm, swollen, crusty areas with discharge were present below the mandibles.

The differential diagnosis for the skin lesions included external trauma or internal causes, including extension of dental pathology, neoplasia, and fungal disease. The initial treatment plan included preoperative testing (CBC, serum chemistry profile, urinalysis, thoracic radiography, blood pressure monitoring, and electrocardiogram), followed by prepping the facial wounds and assessing the oral cavity during a clinical and radiographic tooth-by-tooth examination. All laboratory and cardiac findings were within normal limits.

Surgical and nonsurgical treatments

The patient was premedicated with hydromorphone at 0.1 mg/kg IM, combined with acepromazine at 0.02 mg/kg IM; induced with propofol at 3 mg/kg IV; and intubated and maintained on 2% isoflurane mixed with oxygen. The body temperature was controlled with the Hot Dog patient warming system (Hot Dog USA).

The skin lesions were gently prepped and cleaned with 0.2% chlorhexidine scrub solution, followed by isopropyl alcohol (Figure 3). The teeth were ultrasonically cleaned and polished. There were bilateral 3 × 1-mm enamel and dentin lesions on the buccal surfaces of the mandibular first molars located 1 to 2 mm above and below the furcation at the cementoenamel junctions (Figure 4).

Intraoral radiographs revealed moderate bone loss around the right and left mandibular first and second incisors (Figure 5). The left mandibular first molar apices radiographically appeared to be resorbed, especially mesially. There was marked periapical lucency extending through the left ventral mandible (Figure 6). The right mandibular first molar also was affected by marked periapical lucency (Figure 7). Based on the clinical and radiographic images, extraction of both the mandibular first molars, as well as some of the mandibular incisors, was indicated (Figure 8).

Concerns included the risk that the mandibles would be fractured intraoperatively or soon after surgery if both first mandibular molars were extracted. After discussion, the owner consented to extraction of the left mandibular first molar and conventional endodontic treatment of the right mandibular first molar. A mandibular nerve block consisting of 0.2 ml of bupivacaine was performed bilaterally to achieve regional local anesthesia.

A left mandibular envelope gingival flap was created using a #15 scalpel blade, and a Freer periosteal elevator was used to expose the underlying coronal buccal alveolus of the left mandibular first molar. A #4 round carbide bur loaded on a sterile saline-irrigated high-speed drill was used to expose the coronal aspect of the underlying roots. The double-rooted mandibular first molar was sectioned with a #701 surgical bur to create single-rooted segments. A freshly sharpened wing-tipped elevator was gently rotated perpendicular to the alveolar margin to help create sufficient mobility to deliver the tooth segments from the oral cavity using extraction forceps. A bone curette was used to remove apparent granulation tissue. The surgical site was then irrigated with 0.12% chlorhexidine solution. The left mandibular second incisor and right mandibular first and third incisors were extracted with the help of a wing-tipped elevator and extraction forceps.

Intraoral radiographs confirmed that the extraction sites were free of root fragments. Alveoloplasty using a #2 carbide round bur loaded on a sterile saline water-cooled high-speed handpiece was performed in all exposed areas to smooth the coronal extent of the alveolus before closure. The incised gingiva was closed with 4-0 monocryl suture using a continuous pattern.

Endodontic treatment of the right mandibular first molar began by using a #2 round carbide bur loaded on a sterile saline-irrigated high-speed drill to access the pulp chambers through a coronal access site. K-files loaded with endodontic stops were used to clean and débride both root canals. Irrigation with diluted sodium hypochlorite and water (50:50) was used to remove debris created in the cleaning and filing process. Filing was stopped when clean dentinal shavings were observed at the access sites. Zinc oxide-eugenol applied with the end of an endodontic file was used as a sealer. The canal was obturated with warmed gutta percha (SuccessFil) and back-filled with gutta percha points. Intraoral radiographs showed complete fill of the vertical canals and incomplete fill of the horizontal canal. Access sites were restored with light-cured composite resin (Figure 9).

The buccal surface defect on the right mandibular first molar also was restored after envelope flap exposure and preparation with a #2 inverted cone bur to remove less than 0.5 mm from the surface of the defect. This was followed with application of self-etch adhesive (Adper Easy Bond, 3M ESPE) and a light-cured flowable composite resin (Filtek Supreme Plus, 3M ESPE). The area was smoothed with a white stone bur (Figure 10).

The dog made an uneventful recovery from anesthesia. The owner was instructed to medicate with clindamycin at 15 mg/kg q12h, firocoxib at 5 mg/kg q24h, and tramadol hydrochloride at 2 mg/kg PO q12h.

Clinically the dog did well after surgery and returned to a dry food diet within 3 weeks. Nine months after surgery, follow-up intraoral radiographs (Figure 11) revealed partial resolution of the periapical lucency around the roots of the left mandibular first molar and the treated right first mandibular molar. Complete radiographic resolution of periapical disease was noted on films exposed and evaluated 2 years after surgery (Figure 12).

Discussion

The dog in this case had bilateral mandibular first molar disease that was secondary to dens invaginatus, also known as dens-in-dente, a developmental malformation that results in the in-folding of the enamel organ into the dental papilla during tooth development.1 Invagination occurs along the crown and/or root.1,2

In humans with teeth affected by dens invaginatus, histologic examination has found that enamel and dentin on the outer tooth are not commonly affected, but enamel covering the invagination is defective. In some areas, enamel and dentin are completely missing, as was suspected in this case, which led to direct communication and resulted in contamination of the oral cavity, bottom of the invagination, and pulp. In humans, bilateral involvement is common.3-7

In human dentistry, dens invaginatus is classified as follows5:

Type I — an enamel-lined invagination within the crown but not extending beyond the cementoenamel junction

Type II — an enamel-lined invagination into the root, beyond the cementoenamel junction and ending as a blind sac

Type III — extension of the enamel-lined invagination through the root to form an additional apical or lateral foramen; usually, there is no direct communication with the pulp

Intraoral radiographs are necessary to evaluate cases of dens invaginatus. Often, calcified lesions are visible in the pulp chambers, as well as signs of apical disease. If there is no evidence of periapical disease, the tooth can be restored and clinically evaluated through follow-up radiography.

Generally, when an invagination that communicates with the pulp is not detected, pulpal necrosis results. Management of dens invaginatus with pulpal involvement includes endodontic treatment or extraction. Root canal therapy can be difficult, considering the anatomic variations that dens invaginatus may present within the root canal system. Complete débridement of the root canal system may be compromised by limited access. In those cases, surgical endodontics or extraction is indicated.1-7

Because there may be a genetic component of the disease, owners with dogs affected by dens invaginatus should be counseled about breeding their pets.